Renewable energy is energy derived from natural resources that can be replenished, such as sunlight, wind, rain, tides, and geothermal heat. The demand for renewable energy has grown substantially with advances in technology and increases in global population. Although fossil fuels provide for the vast majority of energy consumption today, these fuels are non-renewable. The global dependence on these fossil fuels has not only raised concerns about their depletion but also environmental concerns associated with emissions that result from burning these fuels. As a result of these concerns, countries worldwide have been establishing initiatives to develop both large-scale and small-scale renewable energy resources. One of the promising energy resources today is sunlight. Globally, millions of households currently obtain power from solar photovoltaic systems.
In general, concentrated solar technology involves the collection of solar radiation in order to directly or indirectly produce electricity. The three main types of concentrated solar technology are concentrated photovoltaic, concentrated solar power, and solar thermal.
In concentrated photovoltaic (CPV), concentrated sunlight is converted directly to electricity via the photovoltaic effect. Generally, CPV technology uses optics (e.g. lenses or mirrors) to concentrate a large amount of sunlight onto a small area of a solar photovoltaic material to generate electricity. CPV systems are often much less expensive to produce than other types of photovoltaic energy generation because the concentration of solar energy permits the use of a much smaller number of the higher cost solar cells.
In concentrated solar power (CSP), concentrated sunlight is converted to heat, and then the heat is converted to electricity. Generally, CSP technology uses mirrored surfaces in multiple geometries (e.g., flat mirrors, parabolic dishes, and parabolic troughs) to concentrate sunlight onto a receiver. That, in turn, heats a working fluid (e.g. a synthetic oil or a molten salt) or drives a heat engine (e.g., steam turbine). In some cases, the working fluid is what drives the engine that produces electricity. In other cases, the working fluid is passed through a heat exchanger to produce steam, which is used to power a steam turbine to generate electricity.
Solar thermal systems collect solar radiation to heat water or to heat process streams in industrial plants. Some solar thermal designs make use of reflective mirrors to concentrate sunlight onto receivers that contain water or the feed stream. The principle of operation is very similar to concentrated solar power units, but the concentration of sunlight, and therefore the working temperatures, are not as high.
The rising demand for solar power has been accompanied by a rising demand for reflective devices and materials capable of fulfilling the requirements for these applications. Some of these solar reflector technologies include glass mirrors, aluminized mirrors, and metalized polymer films. Of these, metalized polymer films are particularly attractive because they are lightweight, offer design flexibility, and potentially enable less expensive installed system designs than conventional glass mirrors. Polymers are lightweight, inexpensive, and easy to manufacture. In order to achieve metal surface properties on a polymer, thin layers of metal (e.g. silver) are coated on the polymer surface.
One exemplary commercially available solar mirror film is shown schematically in FIG. 1. The solar mirror film 100 of FIG. 1 includes a premask layer 110, a weatherable layer 120 (including, for example, a polymer), a thin, sputter-coated tie layer 140, a reflective layer 150 (including, for example, a reflective metal such as silver), a corrosion resistant layer 160 (including, for example, a metal such as copper), an adhesive layer 170, and a liner 180. The film of FIG. 1 is typically applied to a support substrate by removing liner 180 and placing adhesive layer 170 adjacent to the support substrate. Premask layer 110 is then removed to expose weatherable layer 120 to sunlight.